Changing lenses

This is probably a stupid question but I will ask anyway. This Prinz 66 enlarger I have does not appear to have a removable lens board, so how do I remove and replace the lens that is currently on it (a Prinz 50mm)? Do I have to remove the condensor lenses to get at the retaining ring or am I overlooking the obvious? The reason I ask is, I want to get a 75-80mm EL Nikkor for printing medium format while the prices and availability are right. I just can't see spending $20 for a Xerox of the instruction manual, since the entire enlarger, lens and baseboard only cost me $10. Thanks all.

You are overlooking the obvious. To unscrew the lens: unscrew the lens. If the enlarger doesn't have a lensboard system, then it has a threaded flange that the lens screws into. No retaining ring required.

Thanks there. I have a gift for overlooking what is right under my nose. Like my dad used to tell me, "If it was a snake it would bite you". He was right of course.